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<a href="intro.html"><h2>SQLite C Interface</h2></a><h2>Memory Allocation Subsystem</h2><blockquote><pre>void *sqlite3_malloc(int);
void *sqlite3_realloc(void*, int);
void sqlite3_free(void*);
</pre></blockquote><p>
The SQLite core uses these three routines for all of its own
internal memory allocation needs. "Core" in the previous sentence
does not include operating-system specific VFS implementation.  The
Windows VFS uses native malloc() and free() for some operations.</p>

<p>The sqlite3_malloc() routine returns a pointer to a block
of memory at least N bytes in length, where N is the parameter.
If sqlite3_malloc() is unable to obtain sufficient free
memory, it returns a NULL pointer.  If the parameter N to
sqlite3_malloc() is zero or negative then sqlite3_malloc() returns
a NULL pointer.</p>

<p>Calling sqlite3_free() with a pointer previously returned
by sqlite3_malloc() or sqlite3_realloc() releases that memory so
that it might be reused.  The sqlite3_free() routine is
a no-op if is called with a NULL pointer.  Passing a NULL pointer
to sqlite3_free() is harmless.  After being freed, memory
should neither be read nor written.  Even reading previously freed
memory might result in a segmentation fault or other severe error.
Memory corruption, a segmentation fault, or other severe error
might result if sqlite3_free() is called with a non-NULL pointer that
was not obtained from sqlite3_malloc() or sqlite3_realloc().</p>

<p>The sqlite3_realloc() interface attempts to resize a
prior memory allocation to be at least N bytes, where N is the
second parameter.  The memory allocation to be resized is the first
parameter.  If the first parameter to sqlite3_realloc()
is a NULL pointer then its behavior is identical to calling
sqlite3_malloc(N) where N is the second parameter to sqlite3_realloc().
If the second parameter to sqlite3_realloc() is zero or
negative then the behavior is exactly the same as calling
sqlite3_free(P) where P is the first parameter to sqlite3_realloc().
sqlite3_realloc() returns a pointer to a memory allocation
of at least N bytes in size or NULL if sufficient memory is unavailable.
If M is the size of the prior allocation, then min(N,M) bytes
of the prior allocation are copied into the beginning of buffer returned
by sqlite3_realloc() and the prior allocation is freed.
If sqlite3_realloc() returns NULL, then the prior allocation
is not freed.</p>

<p>The memory returned by sqlite3_malloc() and sqlite3_realloc()
is always aligned to at least an 8 byte boundary, or to a
4 byte boundary if the <a href="../compile.html#4_byte_aligned_malloc">SQLITE_4_BYTE_ALIGNED_MALLOC</a> compile-time
option is used.</p>

<p>In SQLite version 3.5.0 and 3.5.1, it was possible to define
the SQLITE_OMIT_MEMORY_ALLOCATION which would cause the built-in
implementation of these routines to be omitted.  That capability
is no longer provided.  Only built-in memory allocators can be used.</p>

<p>Prior to SQLite version 3.7.10, the Windows OS interface layer called
the system malloc() and free() directly when converting
filenames between the UTF-8 encoding used by SQLite
and whatever filename encoding is used by the particular Windows
installation.  Memory allocation errors were detected, but
they were reported back as <a href="../c3ref/c_abort.html">SQLITE_CANTOPEN</a> or
<a href="../c3ref/c_abort.html">SQLITE_IOERR</a> rather than <a href="../c3ref/c_abort.html">SQLITE_NOMEM</a>.</p>

<p>The pointer arguments to <a href="../c3ref/free.html">sqlite3_free()</a> and <a href="../c3ref/free.html">sqlite3_realloc()</a>
must be either NULL or else pointers obtained from a prior
invocation of <a href="../c3ref/free.html">sqlite3_malloc()</a> or <a href="../c3ref/free.html">sqlite3_realloc()</a> that have
not yet been released.</p>

<p>The application must not read or write any part of
a block of memory after it has been released using
<a href="../c3ref/free.html">sqlite3_free()</a> or <a href="../c3ref/free.html">sqlite3_realloc()</a>.
</p><p>See also lists of
  <a href="objlist.html">Objects</a>,
  <a href="constlist.html">Constants</a>, and
  <a href="funclist.html">Functions</a>.</p>
